Motion-adaptive device for separating luminance signal and color signal

ABSTRACT

A motion detector detects motion of pictures represented by a composite color television signal and generates a motion signal representing the detected motion of pictures. A spatiotemporal filter extracts a color signal from the composite color television signal. A subtractor subtracts the color signal from the composite color television signal and thereby generates a luminance signal. The spatiotemporal filter includes a spatial filter. A pass band of the spatial filler is varied in accordance with the motion signal.

This application is a division of application Ser. No. 07/289,804 filedDec. 27, 1988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a motion-adaptive device for separating aluminance signal and a color signal in color video systems such as colortelevision receivers. Such a signal separation device is generallycalled a Y-signal/C-signal separation filter.

2. Description of the Prior Art

Color television receivers include a filtering device for separatelyderiving a luminance signal (Y signal) and a color signal (carrierchrominance signal, C signal) from a composite color television signal.

Typical motion-adaptive Y/C signal separation devices include twofilters each for separating a luminance signal and a color signal, thefirst filter being responsive to a correlation between lines in a commonpicture and the second filter being responsive to a correlation betweenframes. One of the two filters is selected in accordance with an outputsignal from a motion detector sensing motion of pictures.

Japanese published unexamined patent application No. 61-274493 disclosesa digital decoder which includes a Y/C signal separation circuitresponsive to a variation in a common picture, a Y/C signal separationcircuit responsive to motion of pictures, and a band pass filter. Outputsignals from the two separation circuits and the band pass filer aremixed in accordance with spatial variations and time-dependentvariations in pictures to separately derive a final luminance signal anda final color signal.

The 1987 National Convention Record of the Institute of TelevisionEngineers of Japan includes a paper titled "Motion Detector Using NTSCTwo-Frame Difference and Spatio-Temporal Accumulation" in which time andspace are expanded in relation to the detection of motion of pictures inorder to improve the accuracy of the motion detection.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an excellentmotion-adaptive device for separating a luminance signal and a colorsignal.

It is another object of this invention to provide a reliable motiondetector.

In a first device of this invention, a motion detector detects motion ofpictures represented by a composite color signal and generates a motionsignal representing the detected motion of pictures. A time-directionfilter processes the composite color signal. A variablevertical-direction filter processes the composite color signal. A mixermixes output signals from the time-direction filter and thevertical-direction filter at a mixing rate which depends on the motionsignal. A variable horizontal-direction filter extracts a color signalfrom an output signal of the mixer. A subtracter subtracts the colorsignal from the composite color signal and thereby generates a luminancesignal. A vertical-direction variation detector detects a differencebetween levels of the composite color signal at sampling pointsseparated vertically in a picture. A horizontal-direction variationdetector detects a difference between levels of the composite colorsignal at sampling points separated horizontally in a picture. Passbands of the vertical-direction band pass filter and thehorizontal-direction band pass filter are controlled in accordance withthe motion signal and output signals from the vertical-directionvariation detector and the horizontal-direction variation detector.

In a second device of this invention, a motion detector detects motionof pictures represented by a composite color signal and generates amotion signal representing the detected motion of pictures. Aspatiotemporal filter processes the composite color signal. The signalprocessing in the spatiotemporal filter is varied in accordance with themotion signal. A color signal and a luminance signal are separatelyderived from an output signal of the spatiotemporal filter and thecomposite color signal. The motion detector includes means for derivinga difference between frames of the composite color signal and generatinga difference signal representative of the derived difference, means forderiving an absolute value of the difference signal and generating anabsolute value signal representative of the derived absolute value, afirst nonlinear circuit limiting the absolute value signal, aspatiotemporal low pass filter processing an output signal from thefirst nonlinear circuit, and a second nonlinear circuit limiting anoutput signal from the spatiotemporal low pass filter and converting theoutput signal from the spatiotemporal low pass filter into the motionsignal.

In a third device of this invention, a motion detector detects motion ofpictures represented by a composite color signal and generates a motionsignal representing the detected motion of pictures. A time-directionfilter processes the composite color signal. A vertical-direction filterprocesses the composite color signal. A mixer mixes output signals fromthe time-direction filter and the vertical-direction filter at a mixingrate which depends on the motion signal. A horizontal-direction filterextracts a color signal from an output signal of the mixer. A subtractersubtracts the color signal from the composite color signal and therebygenerates a luminance signal. A pass band of the horizontal-directionfilter is varied in accordance with the motion signal.

A detector of this invention includes means for deriving a differencebetween frames of the composite color signal and generating a differencesignal representative of the derived difference, means for deriving anabsolute value of the difference signal and generating an absolute valuesignal representative of the derived absolute value, a first nonlinearcircuit limiting the absolute value signal, a spatiotemporal low passfilter processing an output signal from the first nonlinear circuit, anda second nonlinear circuit limiting an output signal from thespatiotemporal low pass filter and converting the output signal from thespatiotemporal low pass filter into the motion signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a motion-adaptive device for separating aluminance signal and a color signal according to a first embodiment ofthis invention.

FIG. 2 is a diagram of an arrangement of sampling points in the case ofan NTSC signal.

FIG. 3 is a diagram showing a two-dimensional spatial frequency rangedetected by the vertical direction variation detector of FIG. 1.

FIG. 4 is a diagram showing a two-dimensional spatial frequency rangedetected by the horizontal direction variation detector of FIG. 1.

FIG. 5 is a block diagram of the vertical direction variation detectorof FIG. 1.

FIG. 6 is a block diagram of the horizontal direction variation detectorof FIG. 1.

FIG. 7 is a block diagram of the control signal generator of FIG. 1.

FIG. 8 is a block diagram of the vertical direction band pass filter ofFIG. 1.

FIG. 9 is a diagram showing a variation range of control signals for thevariable band pass filters with respect to the relationship between thehorizontal direction band pass filter and the motion coefficient in theembodiment of FIG. 1.

FIG. 10 is a block diagram of the time direction band pass filter ofFIG. 1.

FIG. 11 is a diagram showing frequency characteristics of the timedirection band pass filter of FIGS. 1 and 10.

FIG. 12 is a block diagram of a motion-adaptive device for separating aluminance signal and a color signal according to a second embodiment ofthis invention.

FIG. 13 is a block diagram of a motion-adaptive device for separating aluminance signal and a color signal according to a third embodiment ofthis invention.

FIG. 14 is a diagram showing input-output characteristics of the firstnonlinear circuit of FIG. 13.

FIG. 15 is a diagram showing operation of the time direction low passfilter in the motion detector of FIG. 13.

FIG. 16 is a diagram showing input-output characteristics of the secondnonlinear circuit of FIG. 13.

FIG. 17 is a block diagram of the spatial low pass filter of FIG. 13.

FIGS. 18(A) and 18(B) are diagrams showing frequency characteristics ofthe spatial low pass filter of FIG. 13 and 17.

FIG. 19 is a block diagram of a motion-adaptive device for separating aluminance signal and a color signal according to a fourth embodiment ofthis invention.

FIG. 20 is a block diagram of a motion-adaptive device for separating aluminance signal and a color signal according to a fifth embodiment ofthis invention.

FIG. 21 is a block diagram of a portion of the motion detector of FIG.20.

FIG. 22 is a diagram showing input-output characteristics or the secondand third nonlinear circuits of FIG. 21.

DESCRIPTION OF THE FIRST PREFERRED EMBODIMENT

With reference to FIG. 1, an input terminal 10 is subjected to a digitalcomposite color television signal which is derived from an analogcomposite color television signal by an analog-to-digital (A/D)converter (not shown). The A/D converter samples the analog compositecolor television signal at a predetermined sampling period T andsequentially converts sampled levels into corresponding digital data.The digital composite color television signal is also referred to as acomposite color signal. The digital composite color television signal isfed via the input terminal 10 to a motion detector 11, a delaycompensating circuit 12, a time direction digital band pass filter (BPF)13, a vertical direction digital band pass filter (BPF) 14 of a variabletype, a vertical direction variation detector 20, and a horizontaldirection variation detector 22.

The motion detector 11 includes frame memories and a subtracter. Themotion detector 11 calculates the difference between data at the samepoints of two different frames and thereby detects the motion ofpictures represented by the input composite color television signal. Anoutput signal from the motion detector 11 represents a motioncoefficient "k" which varies between 0 and 1 in accordance with thedegree of motion of pictures. The output signal from the motion detector11 will be referred to as the motion signal "k" hereinafter. The motiondetector 11 may be of the known type.

The time direction BPF 13 removes high frequency components and lowfrequency components from the input composite color television signalwith respect to motion of pictures between two or more successiveframes. As shown in FIG. 10, the time direction BPF 13 includes aone-frame delay circuit 13a and a subtracter 13b. The composite colortelevision signal is applied to an input terminal of the delay circuit13a and a plus input terminal of the subtracter 13b. An output signalfrom the delay circuit 13b is fed to a minus input terminal of thesubtracter 13b. An output signal from the subtracter 13b is used as theoutput signal from the time direction BPF 13. As shown in FIG. 11, thefrequency characteristics of the time direction BPF 13 correspond to thecurve of the absolute values of a sinusoidal function.

An output signal from the delay compensating circuit 12 which is derivedfrom the input composite color television signal through a delaycompensating process is applied to a plus input terminal of a subtracter18. As will be described hereinafter, a minus input terminal of thesubtracter 18 is subjected to a color signal (C signal). The delaycompensating circuit 12 removes a phase difference or delay timedifference between the color signal applied to the subtracter 18 and thecolor signal components in the composite signal applied to thesubtracter 18 so that the subtracter 18 can extract accurate luminancesignal (Y signal) components. Such a phase difference or delay timedifference is caused by delays in the motion detector 11, the timedirection BPF 13, the vertical direction BPF 14, and a horizontaldirection BPF 16 described hereinafter.

An output signal from the vertical direction BPF 14 is applied to a plusinput terminal of a subtracter 17. A minus input terminal of thesubtracter 17 is subjected to an output signal from the time directionBPF 13. An output signal from the subtracter 17 is applied to a firstinput terminal of a multiplier 19. A second input terminal of themultiplier 19 is subjected to the motion signal "k". An output signalfrom the multiplier 19 is applied to a first input terminal of an adder21. A second input terminal of the adder 21 is subjected to the outputsignal from the time direction BPF 13. The combination of the subtracter17, the multiplier 19, and the adder 21 serves to mix the output signalsfrom the BPFs 13 and 14 at a rate which depends on the motioncoefficient "k".

An input terminal of a horizontal direction digital band pass filter(BPF) 16 of a variable type is subjected to an output signal from theadder 21 which corresponds to a mixture of the output signals from theBPFs 13 and 14. The horizontal direction BPF 16 processes the inputsignal into a color signal (a carrier chrominance signal) C. The colorsignal C is applied to a minus input terminal of the subtracter 18 andan output terminal 32.

The subtracter 18 generates a luminance signal Y in accordance with theoutput signal from the delay compensating circuit 12 and the colorsignal C. Specifically, the luminance signal Y corresponds to data whichare equal to data of the output signal from the delay compensatingcircuit 12 minus data of the color signal C.

The vertical direction variation detector 20 calculates the differencebetween data at vertically separated sampling points in a picture andgenerates a signal representative of the calculated difference. Theoutput signal from the detector 20 is fed to a control signal generator24. The horizontal direction variation detector 22 calculates thedifference between data at horizontally separated sampling points in apicture and generates a signal representative of the calculateddifference. The output signal from the detector 22 is fed to the controlsignal generator 24.

The control signal generator 24 generate two primary control signals"mv" and "mh" on the bais of the output signals from the detectors 20and 22. The first primary control signal "mv" is fed to a first inputterminal of a multiplier 23. A second input terminal of the multiplier23 is subjected to the motion signal "k". The multiplier 23 generates afinal control signal "kmv" which corresponds to the primary controlsignal "mv" multiplied by the motion signal "k". The final controlsignal "kmv" is applied to the vertical direction BPF 14.Characteristics of the vertical direction BPF 14 are varied inaccordance with the final control signal "kmv". The second primarycontrol signal "mh" is fed to a first input terminal of a multiplier 25.A second input terminal of the multiplier 25 is subjected to the motionsignal "k". The multiplier 25 generates a final control signal "kmh"which corresponds to the primary control signal "mh" multiplied by themotion signal "k". The final control signal "kmh" is applied to thehorizontal direction BPF 16. Characteristics of the horizontal directionBPF 16 are varied in accordance with the final control signal "kmh".

An NTSC composite color signal is sampled at a frequency which equalsfour times the color subcarrier frequency fsc. As shown in FIG. 2, thesampled data series takes a two-dimensional arrangement in a picturescreen. In FIG. 2, black and white circles denote respective samplingpoints.

The vertical direction variation detector 20 and the horizontaldirection variation detector 22 are designed so that they areinsensitive to the color subcarrier which is a dc component of the colorsignal. Specifically, in respect of the data at the point "c" of FIG. 2,the vertical direction variation detector 20 calculates the absolutevalue of the difference between the data at the points "a" and "e" ofFIG. 2. In respect of the data at the point "c" of FIG. 2, thehorizontal direction variation detector 22 calculates the absolute valueof the difference between the data at the points "b" and "d" of FIG. 2.

FIG. 3 shows characteristics of the vertical direction variationdetector 20. In FIG. 3, the hatched region corresponds to the spatialfrequency range detected by the vertical direction variation detector20. FIG. 4 shows characteristics of the horizontal direction variationdetector 22. In FIG. 4, the hatched region corresponds to the spatialfrequency range detected by the horizontal direction variation detector22. As understood from FIGS. 3 and 4, the detected spatial frequencyranges extend outside the point of the color subcarrier. In addition, asunderstood from FIGS. 3 and 4, high frequency components of theluminance signal and also high frequency components of the color signalcan be detected. In FIGS. 3 and 4, the vertical spatial frequency isrepresented in unit of cycle/height (c/h).

As shown in FIG. 5, the vertical direction variation detector 20includes a subtracter 40, a two-line delay circuit 42, and anabsolute-value converter 43. The composite color television signal isapplied to a minus input terminal of the subtracter 40 and an inputterminal of the delay circuit 42. An output signal from the delaycircuit 42 is applied to a plus input terminal of the subtracter 40. Thedelay circuit 42 delays the input composite color television signal by aperiod corresponding to two horizontal scanning periods (2H). Thesubtracter 40 calculates the difference between the delayed signal andthe non-deleyed signal which correspond to the data at the points "a"and "e" of FIG. 2. The absolute-value converter 43 calculates theabsolute value of the data difference outputted from the subtracter 40.An output signal from the absolute-value converter 43 which representsthe calculated absolute value is fed to the control signal generator 24(see FIG. 1).

As shown in FIG. 6, the horizontal direction variation detector 22includes a subtracter 44, a four-sample delay circuit 46, and anabsolute-value converter 47. The composite color television signal isapplied to a minus input terminal of the subtracter 44 and an inputterminal of the delay circuit 46. An output signal from the delaycircuit 46 is applied to a plus input terminal of the subtracter 44. Thedelay circuit 46 delays the input composite color television signal by aperiod corresponding to four sampling periods (4T). The subtracter 44calculates the difference between the delayed signal and the non-deleyedsignal which correspond to the data at the points "b" and "d" of FIG. 2.The absolute-value converter 47 calculates the absolute value of thedata difference outputted from the subtracter 44. An output signal fromthe absolute-value converter 47 which represents the calculated absolutevalue is fed to the control signal generator 24 (see FIG. 1).

As shown in FIG. 7, the control signal generator 24 includes latches 48and 52, and a read-only memory (ROM) 50. The latch 48 receives data fromthe variation detectors 20 and 22. The data fed from each of thevariation detectors 20 and 22 to the latch 48 have a plurality of bits,for example, 6 bits. The latch 48 combines the received data into anaddress signal outputted to the ROM 50. The address signal has aplurality of bits, for example, 12 bits. A set of predetermined controlsignal data are stored in respective storage locations of the ROM 50.The control signal data are read out from the storage location of theROM 50 which is designated by the address signal fed from the latch 48.Accordingly, the ROM 50 generates the control signal data in accordancewith the output signals from the variation detectors 20 and 22. Thecontrol signal data are transferred from the ROM 50 to the latch 52. Thelatch 52 divides the received control signal data into two primarycontrol signals "mv" and "mh" which are fed to the multipliers 23 and 25respectively. The control signal data preferably have four or more bits.In the case where the control signal data have 8 bits, each of theprimary control signals has 4 bits.

The vertical direction BPF 14, the horizontal direction BPF 16, and thecontrol signal data outputted from the ROM 50 are designed so that thecharacteristics of the BPFs 14 and 16 will basically depend on thedifferences or variations detetected by the variation detectors 20 and22 in the following manner. In the case where the data difference in thevertical direction is greater than the data difference in the horizontaldirection, the pass band of the vertical direction BPF 14 is widenedwhile the pass band of the horizontal direction BPF 16 is narrowed. Inthe opposite case, the pass band of the vertical direction BPF 14 isnarrowed while the pass band of the horizontal direction BPF 16 iswidened. In the case where the data difference in the vertical directionand the data difference in the horizontal direction are substantiallyequal, the pass bands of the BPFs 14 and 16 are made similar to eachother. Since each of the control signals to the BPFs 14 and 16 has aplurality bits as understood from the previous description, thecharacteristics of the BPFs 14 and 16 can be varied among closelydifferent multi-states. Accordingly, it is possible to finely andsmoothly control the characteristics of the BPFs 14 and 16.

Generally, in cases where both of a variation in the vertical directionand a variation in the horizontal direction are great, cross color tendsto occur. Accordingly, in such cases, both of the pass bands of the BPFs14 and 16 are narrowed to adequately suppress the cross color. When bothof the luminance and the color vary greatly, the narrow pass bands ofthe BPFs 14 and 16 cause a narrow color band and increase dotinterference (dot crawl). Generally, in a picture pattern having suchgreat variations in luminance and color, the narrow color band and thedot interference are masked by variations in the luminance signal andare thus inconspicuous while the cross color is conspicuous. In view ofthis fact, the BPFs 14 and 16 are controlled mainly to suppress thecross color.

The control of the BPFs 14 and 16 will be described further hereinafter.As described previously, the primary control signals "mv" and "mh" aremultiplied by the motion signal "k" to generate the final controlsignals "kmv" and "kmh". The data of the primary control signals "mv"and "mh" are variable between 0 and 1. As described previously, the dataof the motion signal "k" is also variable between 0 and 1. Specifically,the data of the motion signal "k" varies from 0 to 1 as the degree ofmotion of pictures increases. The data of the motion signal "k" areequal to 0 when pictures are stationary or still. The data of the motionsignal "k" are equal to 1 when the degree of motion of pictures ismaximized. The BPFs 14 and 16 are designed so that the pass bands of theBPFs 14 and 16 will be maximized when the data of the final controlsignals " kmv" and "kmh" correspond to 0 and will be minimized when thedata of the final control signals "kmv" and "kmh" correspond to 1.

When the data of the motion signal "k" are equal to 1, the output signalfrom the vertical direction BPF 14 is transmitted to the horizontaldirection BPF 16 via the subtracter 17 and the adder 21 withoutundergoing the attenuation by the multiplier 19. In addition, when thedata of the motion signal "k" are equal to 1, the primary controlsignals "mv" and "mh" pass through the multipliers 23 and 25 withoutundergoing the attenuation by the multipliers 23 and 25 so that thefinal control signals "kmv" and "kmh" are in exact agreement with theprimary control signals "mv" and "mh".

As shown in FIG. 9, when the motion coefficient "k" equals 0, that is,when pictures are stationary or still, the pass bands of the verticaldirection and horizontal direction BPFs 14 and 16 are maximizedindependent of conditions of the composite color television signal whichoccurs within a field. As the motion coefficient "k" increases, that is,as the degree of motion of pictures increases, the pass bands of theBPFs 14 and 16 are narrowed. In this case, the pass bands of the BPFs 14and 16 depend on conditions of the composite color television signalwhich occurs within a field. Accordingly, the pass bands of the BPFs 14and 16 are controlled optimally in accordance with three-dimensionalconditions of the composite color television signal along the time axis,the horizontal axis, and the vertical axis.

It is preferable that the primary control signals "mv" and "mh" and themotion signal "k" have 4 bits. The multipliers 23 and 25 are preferablyof 4-bit by 4-bit type.

As shown in FIG. 8, the vertical direction BPF 14 includes a one-linedelay circuit 54a and a one-sample delay circuit 56a into which thecomposite color television signal is inputted. The delay circuit 54adelays the input signal by a period corresponding to one horizontalscanning period (1H). The delay circuit 56a delays the input signal by aperiod corresponding to one sampling period (1T). The output signal fromthe delay circuit 54a is fed to a one-line delay circuit 54b and aone-sample delay circuit 56b. The delay circuit 54b delays the inputsignal by a period corresponding to one horizontal scanning period (1H).The delay circuit 56b delays the input signal by a period correspondingto one sampling period (1T). The output signal from the delay circuit54b is fed to a one-line delay circuit 54c and a one-sample delaycircuit 56c. The delay circuit 54c delays the input signal by a periodcorresponding to one horizontal scanning period (1H). The delay circuit56c delays the input signal by a period corresponding to one samplingperiod (1T). The output signal from the delay circuit 54c is fed to aone-line delay circuit 54d and a one-sample delay circuit 56d. The delaycircuit 54d delays the input signal by a period corresponding to onehorizontal scanning period (1H). The delay circuit 56d delays the inputsignal by a period corresponding to one sampling period (1T). The outputsignal from the delay circuit 54d is fed to a one-sample delay circuit56e. The delay circuit 56e delays the input signal by a periodcorresponding to one sampling period (1T). The output signals from thedelay circuits 56a, 56b, 56c, 56d, and 56e are applied to a first inputterminal of an adder 58b, a first input terminal of an adder 58a, a plusinput terminal of a subtracter 60a, a second input terminal of the adder58a, and a second input terminal of the adder 58b respectively. Theadders 58a and 58b are of the type, dividing the sum of the input databy two and outputting the resultant data. The output signal from theadder 58a is applied to a minus input terminal of the subtracter 60a.The subtracter 60a is of the type, dividing the difference between theinput data by two and outputting the resultant data. The output signalfrom the subtracter 60a is fed to a one-sample delay circuit 56f. Thedelay circuit 56f delays the input signal by a period corresponding toone sampling period (1T). The output signal from the delay circuit 56fis applied to a first input terminal of an adder 58c. The output signalfrom the adder 58b is applied to a plus input terminal of a subtracter60b. A minus input terminal of the subtracter 60b is subjected to theoutput signal from the delay circuit 56c. The subtracter 60b is of thetype, dividing the difference between the input data by four andoutputting the resultant data. The output signal from the subtracter 60bis applied to a one-sample delay circuit 56g. The delay circuit 56gdelays the input signal by a period corresponding to one sampling period(1T). The output signal from the delay circuit 56g is fed to a firstinput terminal of a multiplier 62. A second input terminal of themultiplier 62 is subjected to the final control signal "kmv" outputtedfrom the multiplier 23 (see FIG. 1). The multiplier 62 calculates avalue which equals the output data from the delay circuit 56g multipliedby a variable coefficient "ko". The coefficient "ko" varies between -3/4and +3/4 in accordance with the final control signal "kmv". The outputsignal from the multiplier 62 is applied to a second input terminal ofthe adder 58c. The output signal from the adder 58c is fed to thehorizontal direction BPF 16 (see FIG. 1). The pass band width of thevertical direction BPF 14 is varied with the coefficient "ko". Withrespect to a variation in the coefficient "ko" between -3/4 and +3/4,the maximal pass band width is approximately twice the minimal pass bandwidth.

The horizontal direction BPF 16 is similar to the vertical direction BPF14 of FIG. 8 except that the delay times determined by delay circuits54a-54d correspond to two sampling periods (2T).

DESCRIPTION OF THE SECOND PREFERRED EMBODIMENT

FIG. 12 shows a second embodiment of this invention which is similar tothe embodiment of FIGS. 1-11 except that a vertical direction low passfilter (LPF) 26 is connected between the multiplier 23 and the verticaldirection BPF 14 and that a horizontal direction low pass filter (LPF)28 is connected between the multiplier 25 and the horizontal directionBPF 16.

Control signals "kmv" and "kmh" outputted from multipliers 23 and 25 areapplied to a vertical direction BPF 14 and a horizontal direction BPF 16via the vertical direction LPF 26 and the horizontal direction LPF 28respectively. The characteristics of the LPFs 26 and 28 are designed soas to depend on the directions along which the BPFs 14 and 16 filter thesignals, that is, the objective directions of filtering in the BPFs 14and 16 respectively. This design of the LPFs 26 and 28 allows a smoothvariation in the characteristics of the BPFs 14 and 16 and also preventsthe filtered signals from being unacceptably discontinuous.

DESCRIPTION OF THE THIRD PREFERRED EMBODIMENT

With reference to FIG. 13, an input terminal 110 is subjected to adigital composite color television signal which is derived from ananalog composite color television signal by an analog-to-digital (A/D)converter (not shown). The A/D converter samples the analog compositecolor television signal at a predetermined sampling period T andsequentially converts sampled levels into corresponding digital data.The digital composite color television signal is also referred to as acomposite color signal.

The digital composite color television signal is fed via the inputterminal 110 to a motion detector 112. The motion detector 112 includes524H delay circuits 114 and 120, and 1H delay circuits 116 and 118 whichtogether form a 2-frame delay circuit. It should be noted that 1Hcorresponds to 1 line. The 2-frame delay circuit derives a 2-framedelayed composite color signal from the input composite color signal.The non-delayed composite color signal and the 2-frame delayed compositecolor signal are fed to a subtracter 122, which derives a differencesignal representing the difference between the non-delayed and delayedcomposite color signals. The delay circuits 114, 116, 118, and 120 arestructural elements of the motion detector and are also structuralelements of a time direction band pass filter (BPF) and a verticaldirection band pass filter (BPF) described hereinafter.

The difference signal outputted from the subtracter 122 is fed to anabsolute-value converter 124 and is thereby converted into an absolutevalue signal representing the absolute value of the data of thedifference signal. The absolute value signal is fed via a firstnonlinear circuit 126 to a 525H delay circuit 128 and a first inputterminal of a selection circuit 130. An output signal from the delaycircuit 128 is fed to a second input terminal of the selection circuit130. The delay circuit 128 and the selection circuit 130 form a timedirection low pass filter (LPF). The selection circuit 130 is of theknown type, selecting the greater of the two input signals and passingthe selected input signal. An output signal from the selection circuit130 is fed to a second nonlinear circuit 134 via a spatial low passfilter (LPF) 132. The nonlinear circuit 134 outputs a motion signalrepresenting a motion coefficient "k". The motion signal is applied to amultiplier 152. The spatial LPF 132 is composed of a cascade combinationof a vertical direction LPF and a horizontal direction LPF.

A signal which appears a tap between the delay circuits 114 and 116 isfed to a first input terminal of an adder 136. A signal which appears atap between the delay circuits 118 and 120 is fed to a second inputterminal of the adder 136. The adder 136 adds the data of the two inputsignals and divides the resultant data sum by two. The non-delayedcomposite color signal and the 2-frame delayed composite color signaloutputted from the delay circuit 120 are added by an adder 138. Theadder 138 is of the type, dividing the resultant sum by two. A signalwhich appears at a tap between the delay circuits 116 and 118 is fed toplus input terminals of subtracters 140 and 142, and is fed via a delaycompensating circuit 146 to a plus input terminal of a subtracter 158.An output signal from the adder 136 is applied to a minus input terminalof the subtracter 140. An output signal from the adder 138 is applied toa minus input terminal of the subtracter 142. The subtracters 140 and142 are of the type, calculating the difference between the data of thetwo input signals and dividing the resultant data difference by two. Anoutput signal from the subtracter 140 is fed to a delay compensatingcircuit 144 composed of a delay circuit. An output signal from thesubtracter 142 is fed to a delay compensating circuit 148 composed of adelay circuit. An output signal from the delay compensating circuit 144is applied to a plus input terminal of a subtracter 150. An outputsignal from the delay compensating circuit 148 is applied to a minusinput terminal of the subtracter 150 and a first input terminal of anadder 154. The multiplier 152 multiplies the data of an output signalfrom the subtracter 150 by the motion coefficient "k". An output signalfrom the multiplier 152 is applied to a second input terminal of theadder 154. The adder 154 adds the data of the two input signals. Anoutput signal from the adder 154 is fed to a horizontal direction bandpass filter (BPF) 156. The horizontal direction BPF 156 is preferablycomposed of a known transversal filter having a 3.58 MHz pass band. Thehorizontal direction BPF 156 extracts a color signal C from the inputsignal. The color signal C is applied to an output terminal 162 and aminus input terminal of the subtracter 158. The subtracter 158 subtractsthe color signal components from the composite color signal and therebyderives a luminance signal Y fed to an output terminal 160.

The delay compensating circuits 144, 146, and 148 compensate delay timescaused by the spatial LPF 132 which is described in detail hereinafter.For example, each of the delay compensating circuits 144, 146, and 148includes a flip-flop and a line memory.

The delay circuits 116 and 118, the adder 136, and the subtracter 140form a vertical direction BPF. The delay circuits 114, 116, 118, and120, the adder 138, and the subtracter 142 form a time direction BPF.The time direction BPF and the vertical direction BPF have a linearphase relationship.

The arrangement except the motion detector 112 is basically similar tothe corresponding portion of known Y/C signal separation devices (forexample, see Japanese published examined patent application No.61-58079). The structure of the motion detector 112 is new. Another newpoint of the signal separation device of FIG. 13 is that the outputsignals from the time direction BPF and the vertical direction BPF aremixed at a rate which is varied in accordance with the motioncoefficient "k". In known Y/C signal separation devices, one of theoutput signals from the BPFs is selected by a switch in accordance withthe motion of pictures.

The motion detector 112 will be described further hereinafter. Asdescribed previously, the subtracter 122 generates the difference signalwhich represents the difference between the non-delayed composite colorsignal and the 2-frame delayed composite color signal.

The 2-frame delay circuit which is composed of the delay circuits 114,116, 118, and 120 has five taps. The portions of the 2-frame delaycircuit are used to form the time direction BPF and the verticaldirection BPF via these taps.

The difference signal which is outputted from the subtracter 122 isconverted by the absolute value circuit 124 into the absolute valuesignal representing the absolute value of the data of the differencesignal. The absolute value signal is inputted into the first nonlinearcircuit 126.

FIG. 14 shows input-output characteristics of the first nonlinearcircuit 126. As shown in FIG. 14, the output signal level remains 0 whenthe input signal level is equal to or smaller than 4 which correspondsto a noise level. The output signal level increases linearly from 0 to 1as the input signal level increases from 4 to 16. The output signallevel remains 1 which corresponds to a saturation level when the inputsignal level is equal to or greater than 16. The first nonlinear circuit126 functions to convert the difference between data at each dot ofsuccessive frames into a fully useful signal. Accordingly, in thefunction of the first nonlinear circuit 126, small differences areignored and large differences are limited so that the motion of picturescan be detected substantially independent of the degree of the amplitudeof pictures. The limitation on the difference suppresses erroneousoperation due to pulse noises. It is preferable that the output signalfrom the first nonlinear circuit 126 has 2 bits (varible among 4different levels) or 4 bits (variable among 16 different levels).

The output signal from the first nonlinear circuit 126 is inputted intoa spatiotemporal filter including a time direction LPF and a spatialLPF. The time direction LPF is composed of the delay circuit 128 and theselection circuit 130. The time direction LPF is used to detect avariation at a central tap which can not be detected on the basis of thedifference between frames separated at an interval corresponding to 2frames. The central tap corresponds to a junction between the delaycircuits 116 and 118. The 1-frame delayed difference signal which isgenerated by the delay circuit 128 is additionally used in the motiondetection so that a motion can be detected on the basis of whether ornot a variation occurs in at least one of signals appearing at threetaps which correspond to the input terminal of the delay circuit 114,the junction between the delay circuits 116 and 118, and the outputterminal of the delay circuit 120 respectively.

The function of the time direction LPF will be described further withreference to FIG. 15. When a vertical line of a given width moveshorizontally at a constant speed in a picture screen, the input signalscorresponding to respective fields vary as shown in FIG. 15. Thedetection signal which is derived by the detection using the differencebetween frames separated at a two-frame interval lacks a central motiondetection data present in the detection signal derived by idealdetection. If such a drawback is removed by an infinite impulse responsefilter using a field delay circuit, the level of the target motiondetection data is considerably smaller than that obtained in the idealdetection and spurious motion detection data result from unnecessaryfield components. In the case where the previously-mentioned drawback isremoved by a finite impulse response filter using a frame delay circuit,that is, in the case of this embodiment, appropriate motion detection isperformed with respect to the three taps although an unnecessary motiondetection data corresponding to one frame is generated. The selectioncircuit 130 selects the greater of the non-delayed and delayeddifference signals and passes the selected difference signal to thespatial LPF 132. It should be noted that the selection circuit 130 maybe replaced with an adder adding the non-delayed and delayed differencesignals.

The spatial LPF 132 is used to detect the degrees of variations at dotswithin a predetermined picture region in order to determine the motionof pictures. The spatial LPF 132 and the second nonlinear circuit 134determine the motion of pictures on the basis of the degrees ofvariations of respective dots and on the basis of the number of dotssubjected to variations in the predetermined picture region. This motiondetection is insensitive to an isolated local variation even if thevariation is great. Accordingly, the motion detection is protected frompulse noises and small shifts of edges of pictures. The motion detectionis sensitive to a variation occurring over a wide picture region even ifthe variation has a small amplitude.

As shown in FIG. 17, the spatial LPF 132 includes 1H delay circuits 132aand 132b, 2T delay circuits 132c and 132d, and adders 132e, 132f, 132g,and 132h. The 1H delay circuits 132a and 132b, and the adders 132e and132f are connected to form a vertical direction LPF subjected to aninput signal. The 2T delay circuits 132c and 132d, and the adders 132gand 132h are connected to form a horizontal direction LPF. The verticaldirection LPF and the horizontal direction LPF are connected in cascade.The horizontal direction LPF generates a filter output signal of thespatial LPF 132. The adders 132e-132h are of the type, adding input dataand dividing the resultant data sum by two. As shown in FIGS. 18(A) and18(B), the spatial LPF 132 passes low frequency components in verticaland horizontal frequency ranges. In FIG. 18(B), the character "fsc"denotes the color subcarrier frequency.

FIG. 16 shows input-output characteristics of the second nonlinearcircuit 134. As shown in FIG. 16, the output signal level remains 0 whenthe input signal level is equal to or smaller than a first predeterminedlevel. The output signal level increases linearly from 0 to 1 as theinput signal level increases from the first predetermined level to asecond predetermined level. The output signal level remains 1 whichcorresponds to a saturation level when the input signal level is equalto or greater than the second predetermined level. Accordingly, theinput signal whose level is equal to or smaller than the firstpredetermined level is omitted from the motion detection. On the otherhand, the input signal whose level is equal to or greater than thesecond predetermined level is fully regarded as motion of pictures. Theoutput signal from the first nonlinear circuit 126 has a plurality ofbits as described previously and the spatial filter 132 has a gentleresponse curve so that the processing for moving pictures and theprocessing for stationary pictures can be changed smoothly.

As described previously, the spatial LPF 132 removes a local variationwhich occurs at an isolated point in a picture. Signal componentscorresponding to white noises are transformed by the first nonlinearcircuit 126 into pulses, which are smoothed by the subsequentspatiotemporal filter. As a result, the level of white noise componentsis held smaller than the lower predetermined level in the secondnonlinear circuit 134 and thus the noise components are cut off by thesecond nonlinear circuit 134. Signal components corresponding to pulsenoises and shifts of picture edges are limited in level by the firstnonlinear circuit 126 and are then decreased in level by the timedirection LPF and the spatial LPF 132 so that they are cut off by thesecond nonlinear circuit 134.

It should be noted that the output signal from the first nonlinearcircuit 126 may have a single bit and the spatial LPF 132 may have arectangular response curve. In this case, the motion of pictures isdetected only on the basis of the number of dots subjected to variationsin a tap region of the spatial LPF 132.

In the case where an analog composite color signal is sampled at afrequency which equals four times the color subcarrier frequency, thetaps of the spatial LPF 132 are preferably chosen to define a pictureregion whose vertical dimension corresponds to 3 to 5 lines and whosehorizontal dimension corresponds to 3 to 11 dots. This picture regioncontains 21 to 55 dots. The processing bit number of the spatial LPF 132is preferably chosen to correspond to the bit number of the firstnonlinear circuit 126.

It should be noted that this embodiment may be modified in variousmanners. In an example of such modifications of the embodiment, the timedirection LPF which includes the delay circuit 128 and the selectioncircuit 130 is omitted and the output signal from the first nonlinearcircuit 126 is directly fed to the spatial LPF 132.

DESCRIPTION OF THE FOURTH PREFERRED EMBODIMENT

With reference to FIG. 19, an input terminal 210 is subjected to adigital composite color television signal which is derived from ananalog composite color television signal by an analog-to-digital (A/D)converter (not shown). The A/D converter samples the analog compositecolor television signal at a predetermined sampling period andsequentially converts sampled levels into corresponding digital data.The digital composite color television signal is also referred to as acomposite color signal. The digital composite color television signal isfed via the input terminal 210 to a motion detector 212, a timedirection filter 214, and a vertical direction filter 216, and a plusinput terminal of a subtracter 232.

The motion detector 212 includes frame memories and a subtracter. Themotion detector 212 calculates the difference between data at the samepicture elements of equally separated frames and thereby detects themotion of pictures represented by the input composite color televisionsignal. An output signal from the motion detector 212 represents amotion coefficient "k" which varies between 0 and 1 in accordance withthe degree of motion of pictures. The output signal from the motiondetector 212 will be referred to as the motion signal "k" hereinafter.It is preferable that the motion detector 212 is similar to the motiondetector 112 of FIG. 13.

The time direction filter 214 processes the input composite colortelevision signal in filtering operation along a time direction parallelwith intervals between frames. Specifically, the time direction filter214 operates on the basis of a correlation between two or moresuccessive frames. The vertical direction filter 216 processes the inputcomposite color television signal in filtering operation along thevertical direction in a field. A multiplier 218 multiplies the outputsignal from the time direction filter 214 by a factor of "1-k" which iscalculated from the motion signal "k". A multiplier 220 multiplies theoutput signal from the vertical direction filter 216 by a factor of "k"given by the motion signal "k". Output signals from the multipliers 218and 220 are added by an adder 222.

An output signal from the adder 222 is fed to a multiplier 226 and avertical direction band pass filter (BPF) 224. The multiplier 226multiplies the output signal from the adder 222 by a factor of "1-k"which is calculated from the motion signal "k". The horizontal directionBPF 224 processes the input signal in band pass filtering operationalong the horizontal direction in a field. A multiplier 228 multipliesthe output signal from the horizontal direction BPF 224 by a factor of"k" given by the motion signal "k". Output signals from the multipliers226 and 228 are added by an adder 230 and are thereby combined into acolor signal C applied to an output terminal 234. The subtracter 232subtracts the color signal C from the composite color television signaland thereby generates a luminance signal Y applied to an output terminal236.

As the degree of motion of pictures increases from its minimum to itsmaximum, the motion coefficient "k" increases from 0 to 1. In the caseof moving pictures corresponding to a relatively great motioncoefficient "k", a larger percentage of the output signal from thevertical direction filter 216 and a smaller percentage of the outputsignal from the time direction filter 214 are mixed by the adder 222,and a larger percentage of the output signal from the horizontaldirection BPF 224 and a smaller percentage of the output signal from theadder 222 are mixed by the adder 230. Accordingly, in this case, thevertical direction filter 216 and the horizontal direction filter 224are more effective than the time direction filter 214 so that the bandof the resulting color signal C is narrowed. In the case ofsubstantially still pictures corresponding to a small motion coefficient"k", a smaller percentage of the output signal from the verticaldirection filter 216 and a larger percentage of the output signal fromthe time direction filter 214 are mixed by the adder 222, and a smallerpercentage of the output signal from the horizontal direction BPF 224and a larger percentage of the output signal from the adder 222 aremixed by the adder 230. Accordingly, in this case, the time directionfilter 214 is more effective than the vertical direction filter 216 andthe horizontal direction filter 224 so that the band of the resultingcolor signal C is widened. In this embodiment, the combination of themultipliers 226 and 228 and the adder 230 enables the pass band of thehorizontal direction BPF 224 to vary in accordance with the degree ofmotion of pictures. This control of the pass band of the horizontaldirection BPF 224 effectively prevents dot interference in stillpictures and cross color in moving pictures.

DESCRIPTION OF THE FIFTH PREFERRED EMBODIMENT

FIG. 20 shows a fifth embodiment of this invention which is similar tothe embodiment of FIG. 19 except for the following design change.

In the embodiment of FIG. 20, a motion detector 212A outputs a motioncoefficient "k1" to multipliers 218 and 220 and outputs a motioncoefficient "k2" to multipliers 226 and 228. Both of the motioncoefficients "k1" and "k2" depend on the degree of motion of picturesand are variable between 0 and 1. The motion coefficients "k1" and "k2"are in a predetermined relationship.

FIG. 21 shows a portion of the motion detector 212A. The motion detector212A is similar to the motion detector 112 of FIG. 13 except that athird nonlinear circuit 134A is added. A second nonlinear circuit 134converts an output signal from a spatial LPF 132 into a motion signal"k1". Input-output characteristics of the second nonlinear circuit 134are denoted by the line "k1" in FIG. 22. The third nonlinear circuit134A converts the output signal from the spatial LPF 132 into a motionsignal "k2". Input-output characteristics of the third nonlinear circuit134A are denoted by the line "k2" in FIG. 22. The motion signal "k2" ischosen so as to enhance the effectiveness of the time direction filter214 in an intermediate picture motion range. Accordingly, moderatemotion of pictures can be accurately detected.

What is claimed is:
 1. A motion-adaptive device for separating aluminance signal and a color signal, comprising:(a) a motion detectordetecting motion of pictures represented by a composite color signal,the motion detector generating a motion signal representing the detectedmotion of pictures; (b) a spatiotemporal filter processing the compositecolor signal; (c) means for varying the signal processing in thespatiotemporal filter in accordance with the motion signal; (d) meansfor separately deriving a color signal and a luminance signal from anoutput signal of the spatiotemporal filter and the composite colorsignal; wherein the motion detector comprises: (a1) means for deriving adifference between frames of the composite color signal and generating adifference signal representative of the derived difference; (a2) meansfor deriving an absolute value of the difference signal and generatingan absolute value signal representative of the derived absolute value;(a3) a first nonlinear circuit limiting the absolute value signal; (a4)a spatiotemporal low pass filter processing an output signal from thefirst nonlinear circuit; and (a5) a second nonlinear circuit limiting anoutput signal from the spatial low pass filter and converting the outputsignal from the spatial low pass filter into the motion signal.
 2. Thedevice of claim 1 wherein the motion detector further comprises atemporal low pass filter connected between the first nonlinear circuitand the spatial low pass filter.
 3. The device of claim 1 wherein thespatiotemporal filter includes a time-direction low pass filter havingtaps for respective frames, and field signals between the taps areunused as taps of a digital filter.
 4. The detector of claim 1 whereinthe difference deriving means comprises a delay circuit delaying thecomposite color signal by a period corresponding to two frames andthereby converting the non-delayed composite color signal into a delayedcomposite color signal, and a subtracter subtracting the non-delayedcomposite color signal from the delayed composite color signal, whereinthe delay circuit comprises a first 524H delay element, a first 1H delayelement, a second 1H delay element, and a second 524H delay elementconnected in cascade, and the first and second 524H delay elements andthe first and second 1H delay elements are used in common as elementsforming the spatiotemporal filter, and wherein the character H denotesone horizontal scanning period.
 5. A motion detector comprising:(a)means for deriving a difference between frames of the composite colorsignal and generating a difference signal representative of the deriveddifference; (b) means for deriving an absolute value of the differencesignal and generating an absolute value signal representative of thederived absolute value; (c) a first nonlinear circuit limiting theabsolute value signal; (d) a spatial low pass filter processing anoutput signal from the first nonlinear circuit; and (e) a secondnonlinear circuit limiting an output signal from the spatial low passfilter and converting the output signal from the spatial low pass filterinto the motion signal.
 6. The detector of claim 5 wherein thedifference deriving means comprises a delay circuit delaying thecomposite color signal by a period corresponding to two frames andthereby converting the non-delayed composite color signal into a delayedcomposite color signal, and a subtracter subtracting the non-delayedcomposite color signal from the delayed composite color signal.
 7. Thedetector of claim 5 wherein the output level of the first nonlinearcircuit remains 0 as the level of the absolute value signal increasesfrom 0 to a first predetermined level corresponding to a noise level,the output level of the first nonlinear circuit increases from 0 to 1 asthe level of the absolute value signal increases from the firstpredetermined level to a second predetermined level, and the outputlevel of the first nonlinear circuit remains 1 as the level of theabsolute value signal increases from the second predetermined level. 8.The detector of claim 5 wherein the output level of the second nonlinearcircuit remains 0 as the level of the output signal from the spatial lowpass filter increases from 0 to a first predetermined levelcorresponding to a noise level, the output level of the second nonlinearcircuit increases from 0 to 1 as the level of the output signal from thespatial low pass filter increases from the first predetermined level toa second predetermined level, and the output level of the secondnonlinear circuit remains 1 as the level of the output signal from thespatial low pass filter increases from the second predetermined level.9. The detector of claim 5 further comprising a temporal low pass filterconnected between the first nonlinear circuit and the spatial low passfilter.
 10. The detector of claim 9 wherein the temporal low pass filtercomprises a delay circuit delaying the output signal from the firstnonlinear circuit by a period corresponding to one frame, and aselection circuit selecting and passing a greater of the output signalfrom the first nonlinear circuit and an output signal from the delaycircuit.